Process for preparing stable polystyrene emulsions



pensions.

Patented Mar. 20, 1951 UNITED STATES PATENT OFFICE PROCESS FOR PREPARINGSTABLE POLYSTYRENE EMULSIONS Forrest H. Norris, Springfield, Mass,assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation ofDelaware No Drawing. Application May 15, 1948, Serial No. 27,361;

6 Claims. I (01. 26023) 1 This invention relates to synthetic resin sus-More particularly, the invention relates to stable aqueous suspensionsof synthetic resins, processes for making said suspensions andparticular dispersing agents for use therein.

Aqueous suspensions of synthetic resins are used in the surface coatingand textile and paper impregnating fields. They comprise syntheticresins in a finely divided state dispersed throughout an aqueous medium.Thesuspensions generally contain a small amount of an agent acting tomaintain the particles in suspension and to prevent them from settlingto the bottom of the container.

Aqueous suspensions of synthetic resins may be made by dispersing finelydivided resins in an aqueous medium containing a dispersing orsuspending agent using mechanical agitation as a means for originallydispersing the resin particles. The suspensions may also be made bypolymerizing an unsaturated monomer or plurality of such monomers inaqueous emulsion in the presence of dispersing or emulsifying agents.The products of the emulsion polymerization process are suspensions ofsolid resin particles in an aqueous medium containing a dispersingagent. r The dispersing agents used in prior processes either haveproduced unstable suspensions or when they produced stable suspensionshave been seriously detrimental to the physical and chemical propertiesof the resin.

It is an object of this invention to provide stable synthetic resinsuspensions. A further object is to provide a process for producingstable synthetic resin suspensions.

Another object is to provide dispersing agents for synthetic resinsuspensions which produce stable dispersions and do not adversely affectthe chemical and physical properties of the resins. Thes and otherobjects are attained by polymerizing unsaturated compounds in aqueousfatty acid.

The following examples are given in illustration and are not intended aslimitations on the scope of this invention. Where parts are mentioned,they are parts by weight.

Example I 6 parts of a vinyl acetate-maleic anhydride copolymer preparedby copolymerizing approximately equimolar proportions of vinyl acetateand maleic anhydride were dissolved with constant agitation at 90 C. in700 parts of water containing 8.4 parts of ammonia. There were thenadded 6 parts of oleic acid and the solution was refluxed at atmosphericpressure until the oleic acid was dissolved. To this solution was added0.2 part of a silicone antifoaming agent to provide an aqueous mediumsuitable for emulsion polymerization.

To the aqueous medium thus prepared were added a mixture of 285 parts ofmonomeric styrene and 90 parts of butyl benzyl phthalate over a periodof minutes. The aqueous medium was maintained at reflux temperature atatmospheric pressure and constant agitation was provided throughout theaddition of the styrene monomer. A solution comprising 0.4 part ofpotassium persulfate and 1 part of ammonium hydroxide in .40 parts ofwater was added to the aqueous medium in eight approximately equalportions over a period of about 2 hours. Re-

fluxing at atmospheric pressure and constant agitation was maintainedthroughout the 2-hour period and continued thereafter until the refluxtemperature rose to about 98-100 C. The reaction was then essentiallycomplete and the product was cooled.

The product was a stable suspension of plasticized polystyrene, theparticles of which were substantially all less than 5 micronsindiameter. The conversion of monomer to polymer was approximately 99.5%complete. The suspension contained about 30% solids by weight,

moved and dried at 100 C. The resultant mat consisted of 72% by weightof plasticized polystyrene and 28% by weight of glass. The fibers werefound to be thoroughly coated and bonded by theresin.

Example II An aqueous emulsifying medium was prepared by dissolving 10parts of sodium hydroxide and 6 parts of a vinyl acetate-maleicanhydride copolymer in 700 parts of water, adding thereto 6 3 parts ofoleic acid, heating the solution at reflux temperature to dissolve theacid and finally incorporating 0.2 part of a silicone antifoaming agent.

To the aqueous medium thus prepared was added slowly a mixture of 285parts of styrene monomer and 90 parts of butyl phthalyl butyl glycollateover a period of about 15 minutes While maintaining the aqueous mediumat reflux tem perature at atmospheric pressure and while providingcontinuous agitation. A solution comprising OA part of potassiumpersulfate and 1 part of ammonium hydroxide in 40 parts of water wasadded to the aqueous medium in eight separate portions distributedevenly over a z ho ur period. Refluxing at atmospheric pressure andconstant agitation was maintained during a 52-hour period and continueduntil the reflux temperature rose to 98-100 C. Th reaction was thenessentially complete and the reaction mixture was cooled.

The product was an aqueous suspension of polymerized styrene plasticizedwith butyl phthalyl butyl glycollate. The size of the polystyreneparticles in the suspension was less than 5 microns. The conversion ofthe styrene monomer to the polymer was about 99.5% complete. Themolecular weight of the polystyrene was greater than 150,000.

The suspension contained about 30% solids by weight, hada viscosity of90 centipoises, a pH of 8.4 and was stable to agitation in a WaringBlendor for more than 5 minutes.

A film prepared from-a portion of the suspension by casting onto a glassplate and evaporating the volatile matter at elevated temperature wasclear, transparent and tough.

A portion of the suspension was diluted to 20% solids with water. Aglass mat was immersed in the diluted suspension, removed and dried atabout 100 C. The product was found 130.comtain 50% resin by weight and.the glass fibers were thoroughly coated and well bonded by the resin.

, Example III was repeated substituting stearic acid for oleic acid. Thesuspension obtained had a viscosity of 200 centipoises at 30% solids, apH of 8.5, and was stable for more than 5 minutes to agitation in aWaring Blendor. A film cast from the suspension was clear, transparent,tough and elastic. V

When suspensions were made by similar methodsby using ammonium oleate, asodium sulfonate of alkyl benzenes or a commercial soap without thevinyl acetate-maleic anhydride copolymer salt, the suspensions wereunstable to agitation, had viscosities of less than 30 centipoises,produced weak, tacky films and showed less than 30 resin pickup on glass"fiber mats based on the weight of the glass fibers When salts of vinylacetate-maleic anhydridecopolymers were usedas the sole dispersingagents it was found substantially impossible to produce suspensionsstable to agitation.

The vinyl ester-maleic anhydride copolymers to be used are made bycopolymerizing a vinyl ester of a lower aliphatic acid such as vinylformate, vinyl acetate, vinyl propionate, vinyl butyrate, vinylvalerate, etc, with maleic anhydride or maleic acidby conventionalpolymerization processes, such as mass, solution, suspension or emulsionmethods. The mol ratio of vinyl ester to maleic anhydride may be variedfrom 1:9 to 9:1. In a preferred embodiment of the invention, the molratio may be varied between 1:1 and 2.5 :l.

A specific example of one method for preparing a specific copolymer isto mix 1 mol of vinyl acetate with 1 mol of maleic anhydride and about1% by weight ofbenzoyl peroxide in a suitable container. The mixture maythen be heated at from 40-200" C. to obtain a solid polymer. may then bepulverized and dissolved in water made alkaline with ammonia or analkali metal hydroxide. I I i p v In a further embodiment of theinvention the maleic anhydride may be partially esterified w ith analcohol and the partial ester copolymerized with the vinyl ester. Foresterification purposes, aliphatic alcohols having from 1 to 20 carbonatoms are preferred. Best results are obtained when the maleic anhydrideis esterified to the extent of from about 5% to about 25% Thecopolymerization of the partial esters of maleic anhydride with thevinyl ester may be carried out by conventional mass, suspension,emulsion and solution methods. V v p o h The amount of vinylester-maleic anhydride copolymer salt may be varied from about 0.1 toabout 5%,,based on the monomer. By varying the amount of the copolymersalt within otherwise identical formulations the viscosityof thesuspensions may be controlled as shown by Examples I and III, wherein6'parts of vinyl acetatemaleic anhydride copolymer per 285 parts ofstyrene monomer gave a suspension having a viscosity of 3000 centipoisesat 30% solids (Example I) where as the viscosity was only 20 centipoisesat 30% solids when the amount of vinyl acetate-maleic anhydridecopolymer was reduced to 2 parts (Example III). The viscosity controldue to the copolymer may be further extended to cover a range of fromabout 10 to about 4000 centipoises.

The viscosity of the suspensions is also afiected by the plasticizerused and by the alkali used as shown in Example II.

The long chain fatty acid salt used as the second dispersing agent maybe an ammonium or alkali metal salt'of a saturated or unsaturatedaliphatic acid containing from about 12 to about '20 carbon atoms. Amongthe salts which may be used are theammonium, lithium, sodium, potassium,rubidium and cesium salts of such acids as lauric, stearic, palmitib,oleic, myristic, ricinoleic, etc. acids. It is preferable, although notnecessary, that the cation used should be the same for both dispersing,agents. The amount of long chain fatty "acid salt used may vary fromabout 0.1 toabout 5% based on the'polymerizable monomer. A preferredrange is from 2-3%.

The method of addition of the two dispersing agents may be varied.Theacid and copolymer may be added to the aqueous phase containing thehydroxide of the desired cation. The salts may be prepared separatelyand then added to the aqueous phase. The "copolymer may be added to theaqueous phase containing the desired base and the acid may be mixed withthe monomer prior to its addition to the aqueous phase.

The solid in place or the styrene shown in the examples,

other polymerizable monomers or a plurality of polymerizable monomersmay be used. To be eifectively polymerized in aqueous emulsions, the

nitrostyrenes, vinyl naphthalene, vinyl diphenyl,

divinyl benzene; vinyl esters, ethers and amides, including vinylacetate, methyl vinyl ether, ethyl vinyl ether, etc. acrylic anda-substituted acrylic acid derivatives including their esters, amides,nitriles such as the alkyl esters of acrylic acid, methacrylic acid,chloracrylic acid, phenyl acrylic acid, methacrylamide, acrylonitrile,methacrylonitrile; derivatives of (Pp-unsaturated dibasic acids such asthe esters, amides and nitriles of maleic, fumaric, itaconic,citraconic, mesaconic, etc. acids; allyl derivatives; vinylidenecompounds, dienes, isoolefines, etc. Two or more of the unsaturatedmonomers may be copolymerized by the process of this invention.

The films produced from the suspensions made according to this inventionvary in toughness, hardness and other physical properties according tothe monomer or monomer mixture used. It may be desirable to plasticizesome of the resins such as polystyrene. It has been found advantageousand practical to incorporate the plasticizer in the emulsion along withthe monomer. Any of the known water-insoluble plasticizers may be usedin proportions to be determined by the degree of softness required.Butyl benzyl phthalate and butyl phthalyl butyl glycollate are shown inthe examples. Other plasticizers such as esters of phthalic, succinic,sebacic, adipic, citric, aconitic, phosphoric acids, aromatichydrocarbons, chlorinated diphenyls, may be used or a mixture ofplasticizers may beused.

The polymerization catalysts shown may be replaced by otherwater-soluble catalysts including hydrogen peroxide, perborates,persulfates,

etc. The amount of catalyst may be varied from about 1 to about 5% basedon the monomer.

Other conventional additives such as dyes,

pigments, natural or synthetic resins, lubricants, waxes, etc. may beadded to the emulsions either prior to or subsequent to thepolymerization reaction.

The polymerization reaction may be varied in several ways. The monomeror monomer mixture may be added in toto to the aqueous phase prior topolymerization or it may be added continuously to' the aqueous phaseover a period of from 10 minutes to 4 hours or more. In the latter eventpolymerization will start with the first addition of monomer and will becontinued for a varying period of time after the monomer has beenentirely added.

The catalyst may be added in toto to the aqueous phase, continually,over the same period of time as the monomer, or batchwise at intervalsduring the polymerization of the monomer. It is preferable to dissolvethe catalyst in water and add it to the polymerization reaction as anaqueous solution. I

The temperature of the polymerization reaction may be varied. For themost rapid polymerization, the reaction medium may be refluxed atatmospheric temperature. However, the temfrom about 10 to about 40%.

'6 perature may be from 20 to 50 degrees Centigrade lower than refluxtemperature if desired.

To produce an emulsion, the reaction ingredients must be agitatedthroughout the reaction. Using the specific combination of dispersingagents of this invention, the rate of agitation is not critical. Usingan anchor type of stirrer, the R. P. M. may vary from less than 50 tomore than 200. The rate of agitation will be determined by type ofagitating means, batch size, reaction vessel design, foaming propertiesof the reactants, temperature, etc.

For styrene emulsion polymerization, the pH of the reaction should be atleast 9. It may be controlled by the use of pH regulators or bufiers.For other monomers and monomer mixtures, other pH ranges may bedesirable. In general, the pH of the emulsion polymerization and thefinal suspension should not be below 8.-

Using the disperSing-- agents of this invention,

the solids content of the final suspension may be varied from about l'toabout 60%. For practical applications, the solids content will Vary Thefinal suspensions may be diluted with water to an infinite extent, e.g., even until a specific gravity of approximately 1 is obtained,without breaking the suspension.

The suspensions of this invention may be made into tough continuousfilms by casting them on a smooth surface such as glass or polishedsteel. They may be sprayed by conventional means such as an ordinaryspray gun to coat or impregnate various materials such as glass, wood,metals, paper and fabrics, or they may be applied to these materials byother means such as roll-coating, dipping, etc.

The combination of dispersing agents of this invention permits theproduction of stable suspensions of polymers and copolymers by theemulsion polymerization process. The viscosity of the suspensions may bevaried as required. Films prepared. from the suspensions are strongerand tougher than films made from suspensions in which other dispersingagents were used or from suspensions made from the resin afterpolymerization. Furthermore, when used as impregnating agents forfabrics such as glass fiber mats, the retention of resins from thesuspensions of this invention is exceptionally high.

It is obvious that many variations may be made in the products andprocesses of this invention without departing from the spirit and scopethereof as defined in the appended claims.

What is claimed is:

l. A process for preparing stable suspensions which comprisespolymerizing parts of styrene with substantially constant agitation inan aqueous medium comprising a water solution containing from 0.1 to 5parts of a compound taken from the group consisting of ammonium andalkali metal salts of a copolymer of a, vinyl ester of a lower aliphaticacid and maleic anhydride and from 0.1 to 5 parts of a compound takenfrom the group consisting of ammonium and alkali metal salts ofmonocarboxylic aliphatic acids containing from 12 to 20 carbon atoms.

2. A process as in claim 1 wherein the vinyl ester is vinyl acetate.

3. A process as in claim 1 aliphatic acidis oleic acid.

4. A process for preparing stable suspensions which comprisespolymerizing 100 parts of a mixture of styrene and an unsaturatedwater-insoluble compound polymerizable therewith with subwherein theC12-C2o stantially: constant agitation. an que us m dium comprising awater solution containing from 0.1 to. 5. parts of a compound taken fromthe group consisting of ammonium and alkali metal salts of a copolymerof maleic, anhydride and a vinyl ester of lower aliphatic acids and from0.1 to parts of a compound taken from the group consisting of ammoniumand alkali metaI salts of monocarboxylic aliphatic, acids containingfrom 12 to 20 carbon atoms.

5. A process for preparing stable suspensions which comprisespolymerizing 100 parts of a mixcure of styrene and a plasticizertherefor with substantially constant agitation in an aqueous mediumcomprising a water solution containing 0,1 to 5' parts of a compoundtaken from the group. consisting of ammonium and alkali metal salts, ofa copolymer of maleic anhydride and a vinyl esterof a lower aliphaticacid and from 0.1 to, 5 parts of a compound taken from the groupconsisting of the ammonium and alkali metal salts of monocar-boxylicaliphatic acids containingfrom 12 to 20 carbon atoms.

OR ES N RRI REFERENCES CITED The following references are of record, inthe file of this patent;

UNITED STATES PATENTS umbe am Date 1 97 ,6 ili ntsc ret a1. r Oct; 9,934 2,3QQ,. .6 et a "Ts-hog Nov. 3, 1.942 2,388 60 Coll ns ""4 --o Nov-6,19 5. 2,553,9 9. W ls n o o r v. s. J une 2 1.9 3

OTHER REFERENCES Braj nikofi Plastics (London) pages 230-238, J .5 .9..2-

1. A PROCESS FOR PREPARING STABLE SUSPENSIONS WHICH COMPRISESPOLYMERIZING 100 PARTS OF STYRENE WITH SUBSTANTIALLY CONSTANT AGITATIONIN AN AQUEOUS MEDIUM COMPRISING A WATER SOLUTION CONTAINING FROM 0.1 TO5 PARTS OF A COMPOUND TAKEN FROM THE GROUP CONSISTING OF AMMONIUM ANDALKALI METAL SALTS OF A COPOLYMER OF A VINYL ESTER OF A LOWER ALIPHATICACID AND MALEIC ANHYDRIDE AND FROM 0.1 TO 5 PARTS OF A COMPOUND TAKENFROM THE GROUP CONSISTING OF AMMONIUM AND ALKALI METAL SALTS OFMONOCARBOXYLIC ALIPHATIC ACIDS CONTAINING FROM 12 TO 20 CARBON ATOMS.